Bonn 2020 – scientific programme
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EP: Fachverband Extraterrestrische Physik
EP 4: Sun and Heliosphere II
EP 4.5: Talk
Wednesday, April 1, 2020, 11:45–12:00, H-HS VIII
Scattering of the electron strahl in the solar wind — •Daniel Verscharen1,2, Benjamin Chandran2,3, Seong-Yeop Jeong1, Chadi Salem4, Marc Pulupa4, and Stuart Bale4,5,6 — 1Mullard Space Science Laboratory, University College London, UK — 2Space Science Center, University of New Hampshire, USA — 3Department of Physics and Astronomy, University of New Hampshire, USA — 4Space Sciences Laboratory, University of California, Berkeley, USA — 5Physics Department, University of California, Berkeley, USA — 6The Blackett Laboratory, Imperial College London, UK
We investigate the scattering of strahl electrons by microinstabilities as a mechanism for creating the electron halo in the solar wind. We develop a mathematical framework for the description of electron-driven microinstabilities and discuss the associated physical mechanisms. We find that an instability of the oblique fast-magnetosonic/whistler (FM/W) mode is the best candidate for a microinstability that scatters strahl electrons into the halo. We derive approximate analytic expressions for the FM/W instability threshold in two different βc regimes, where βc is the ratio of the core electrons’ thermal pressure to the magnetic pressure, and confirm the accuracy of these thresholds through comparison with numerical solutions to the hot-plasma dispersion relation. The comparison of our theoretical results with data from the Wind spacecraft confirms the relevance of the oblique FM/W instability for the solar wind. We make predictions for the electron strahl close to the Sun, which will be tested by measurements from Parker Solar Probe and Solar Orbiter.